It is generally accepted that American steam locomotives achieved thermal efficiencies of around 6% at the drawbar, and there are claims that with not too radical technology, this could have been significantly improved. Porta said American draughting systems (including blastpipe dimensions) ‘could not have been worse’. I am lacking some key bits of data I need for this, and am wondering if anyone in these forums might have access to the data.
The calculation of drawbar efficiencies requires knowledge of three things- engine efficiency (how much steam needed to produce 1 horsepower for an hour), boiler efficiency (how much coal to produce a given amount of steam) and the amount of power that needs to be expended to move the locomotive as a vehicle, which must be subtracted from the cylinder power to get drawbar power.
With regard to engine efficiency, I have a computer programme developed by a very distinguished UK Professor, which calculates engine efficiency from first principles. I have validated this against UK and Altoona test data, and with some caveats that I can share with those interested, it works just fine. What it says is engine efficiency is dominated by the beneficial effect of higher superheat, which generally gets higher at higher steam rates; the next most important factors are blastpipe pressure, which increases detrimentally at high exhaust rates, and cut off. When locomotives are operating in less than 30% cut off, cut off is not such a big deal, but higher values, as required at low speeds and when climbing mo
I believe we need to clarify some terms first. The steam temperatures you mention are not superheat but total steam temperature. Big difference. 250 degrees superheat was considered conservative for modern steam locomotives. Tests of the NYC Niagara and PRR T1 showed superheat temps of well over 300 degrees at their respective boiler pressures (275 and 300 psi).
Another item is the constant IHP as speed increases. Test data indicates that this is not how things work. Most estimating methods compute theoretical IHP as being asymptotic as speed increases. However, actual IHP tends to increase up to about driver diameter plus 10% then starts to decrease.
I’m also suspicious of the very high steaming rates at low speeds for both examples above. Whereas both boilers could probably produce over 100,000 lbs of steam an hour, neither would be particularly efficient at such high rates.
Be very cautious about simplistic ratios when trying to estimate locomotive performance. I’ve seen a bunch of them and almost always they produce only a meaningless average. Worse, they tend to overlook various components that are important to consider in the overall scheme of things. Steam locos are not easy to predict. I’ve used generally accepted industry methods and tweaked them a bit for modern construction and some other items. There are abut 20 equations involved, none of which I would call simplistic. Careful with this… I’m interested but skeptical.
Thanks very much for your response. You are correct to pick me up on the loose use of the word ‘Superheat’; I do of course mean inlet steam temperature not the level of superheat in the steam.
The use of constant IHP in my calculations was just for illustrative purposes. If you use constant steam rate as the basis, then you do indeed get IHP values that asymptote as speed increases. There is a possibility that IHP will decrease if you go above a certain speed at constant steam rate, i.e. efficiency decreases despite the fact the cut off is shortening and expansion ratio improving. UK test plant work was normally not above 80mph, so with your diameter +10% rule, you would not expect to see this, and you don’t except for some hints thereof on older GW railway designs with low clearance volume, where there is serious overcompression at high speeds.
You can use the computer programme to establish when this would occur; it depends on the operating condition. With late UK designs, e.g. the streamlined A4, (80" drivers) it says that at constant steam rate in the normal working range, efficiency begins to plateau around 100mph and shows positive decreases about 120mph. The point is that where this turnover point is can be now be calculated, if you have the detail of the engine dimensions (Lap, lead, clearance volume, port width etc). This is the next layer of detail that I would need to understand about US types, but tens of thousands of calculations all say that from the point of view of gross efficiency, the point in question, these things are second order.
Now in practice locomotives were worked neither at constant steam rate nor constant power of course, and my argument justifying the 5-6% overall thermal efficiency is indeed a bit simplistic. However, I have done lots of work simulating logs of reported steam performance on various main lines (the only US one on which I have sufficent data is the Milwaukee from Chicago to La Crosse), and you can use equations d
Google books has tests of locomotives from the Pennsylvania RR done on the test plant. These are very interesting reads. The PRR testing department tested everything. Even the coal is broken down to its BTU and ash content.
Thanks for the tip- unfortunately the Altoona reports on Google are the ones I have access to! Reports 1-32 were presented to the British Institute of Mechanical Engineers in two bound volumes ca 1925, personally signed by (I think) the PRR CME. These are now in the Science Museum Library in London, disintegrating rapidly. They are wonderful documents, comprehensive data, crystal clear write ups, confident without being overbearing- a model. In terms of testing the PRR was way ahead of the game at the time. I think the 1914 Bulletin 24 on the effects of superheat is one of the most influential ever written; I’m sure Chapelon digested it and in this country, Gresley immediately copied the variations in superheater set up on his own Pacifics in 1926.
Still hoping someone has access to details of the final flowering of US steam from ca 1926-1949
Didn’t the late UP locomotives have Le Maitre exhausts?
Some photos of these show multiple jet nozzles arranged in a circle and the large diameter stack suggests that arrangement. That is at least part of the way towards Porta’s ideas.
Er-hm … if you may pardon my joining your discussion, may I just add a few words?
The UP Jabelmann double chimney arrangement included quadruple blast nozzles each. With that draughting both Challenger and FEF-II could and likely did exceed 100,000 lbs/h steaming rates. However may I ask how backpressure, draught vacuum and efficiency of this or any other draughting arrangement should be calculated indiscriminatingly of design specs?
In paragraph one of your original posting you correctly quote Porta’s saying – yet this must be seen in context. First, as from what I’ve had an oppor
Test reports for both the PRR T1 and NYC Niagara survive, but they are not published for sale. I know they exist because I’ve used them extensively over the years. I believe the Q2 test report also survives, but I’ve not seen it.
A book called Santa Fe’s Big 3, by S. Kip Farrington, has considerable operating data on the last classes of ATSF 4-6-4, 4-8-4 and 2-10-4. I have it and it’s proved to be a good source of information. This book is usually available on line from several used book vendors.
There’s a very good book available in the UK called Dropping the Fire by Phil Atkins. Although this is not technically rigorous, it has exceptionally good write-ups on several US locomotive classes (Niagara, PRR T1, N&W Y6’s…).
Back to the original post. I notice that total evaporative surface is used. I believe this is shortsighted, particularly with US locomotives. After 1930, more locomotives had large combustion chambers, and this altered the proportion of evaporation produced between the direct heating surface and indirect heating surface.
Two examples -
(1) The PRR M1 4-8-2 of the mid 1920’s had PRR’s “standard” grate area of 70 sq. ft. ( used for the K4 4-6-2, L1 2-8-2, I1 2-10-0 and later the K5 4-6-2). However, it had a very large combustion chamber which allowed higher firing and evaporative rates. This increase in furnace volume enabled this improvement
(2) A much later example can be found in N&W’s modification of the interior proportions of its famous Y6 2-8-8-2 compounds in the early 1950s. Initially they had 24 ft flues and a short combustion chamber. This was later modified to 20 ft flues and a 48" extension to the combustion chamber all within the same boiler shell. This produced in increase in the direct HS and a reduction of the indirect HS. The total evap heating surface was reduced, but the
talking about efficiency, how much power could modern “all axle roller-bearings based” steam-engines
produce at the tender’s draw-bar, including mechanicary and air-resistance, actually?
I have never seen a “conversion table”, but starting with your data, maybe ~20%?
So, 4500 DBHP for a FEF-2/3, 4800-5000 DBHP for the Chally? Just as a rule of thumb…
-edit-
Those figures in Mr. Dreyfusshudson’s table talking ~10% ? Is not it awesome, from that point of view that modern diesel-electrics do not do better, regarding shaft power to drawbar.
Er-hm … if you may pardon my joining your discussion, may I just add a few words?
The UP Jabelmann double chimney arrangement included quadruple blast nozzles each. With that draughting both Challenger and FEF-II could and likely did exceed 100,000 lbs/h steaming rates.
I commend you on your work on this topic, and I offer you encouragement in the face of some of the naysayers.
What you offer is an engineering model, that is, a somewhat simplified version of a collection of much more complicated formulas and equations. The purpose of your model is 1) to predict the performance of known steam locomotives, with the view of understanding the rough contribution of various system components – the grate, the evaporative surface area, aerodynamic resistance in the steam circuit, exhaust back pressure, and so on, and 2) armed with the ability of the model to predict known steam locomotives, to make educated guesses regarding what enhanced or improved steam locomotive designs could have done.
The fact that you get into “the ballpark” of the 5-6 percent thermal efficiency often quoted for 20th century U.S. steam, and that you get into that ballpark based on thermodynamic, fluid dynamic, and empirical relationships tells me that leaving aside the naysayers, that the quirks of individual steam engines are unknowable apart from much more complicated formulas, that you indeed have a good model of steam locomotive thermal efficiency and are to be commended for your efforts.
I am sorry I don’t have data or measurements on steam locomotives to contribute. My only suggestions is that the David Wardale 5AT steam locomotive project has a Web site along with links to technical information you could check out (does his prediction of efficiency on the low to mid teens for this proposed design square with your methods?). David Wardale also has this out-of-print book The Red Devil and Other Tales from the Age of Steam – if one could get a copy somehow, I am told it too has considerable technical detail on steam locomotive efficiency.
I commend you on your efforts and look forward to more results from your model.
To Lars Loco: How much power could an all roller bearing axle locmotive have at the drawbar? Well, have you ever ridden on a jetliner? I rode behind Norfolk and Western’s Class “J” 611 several times before the excursion program was stopped, and got that same set-back in the seat when the engineer opened the throttle! Not as much, mind you, but it was certainly there! A “J” could produce 73,300 pounds of tractive effort, can’t tell you the horsepower, none of my books have the answer, but my dear God, what a magnificent machine! If General Lee had one available to him in the 1860’s, along with “Seven-Elevens” and pick-up trucks, the South would have won The War!
do you know Charlie Chaplin´s “The General” ? It shows the most dramatic stunts ever made in movie´s history, now imagine he would have had a 611-class engine available … phew… too though even for Charlie…
To Lars Loco: Oh yeah, I’ve seen “The General”! A very funny movie, but seeing that old 4-4-0 get wrecked on the burning bridge makes my skin crawl! Oh well, at the time it was OK. and the locomotive was due to be scrapped anyway, but I can’t look at it now without thinking of it as the loss of a fine railroad artifact. And doing it to a Class “J” doesn’t even bear thinking about! By the way, I misspoke on the "J"s tractive effort. Post- war modifications brought them up to 80,000 pounds of tractive force, making them the most powerful “Northerns” ever built. Oh, and the Norfolk and Western always called them "J"s, there was no way a Virginia road was going to call them “Northerns”! “Old times there are not forgotten…”
First of all, let me express my appreciation for all the comments you have all made- a very considerable efforts in some cases. Thank you very much indeed. I will try to produce a single response to all these points, starting with some generalities, then getting to specific individual comments and queries later.
Let me start by referring to Feltonhill’s comment ‘I’m not sure where this discussion is going’ and reiterate my hope as to where it might go. What I have done, as Paul Milenkovic observes it to link together a series of engineering models of the key components of drawbar efficiency; engine efficiency, boiler efficiency, and Locomotive resistance (LR); the first is a fully worked through first principles model, the latter based on detailed estimates of the likely magnitude of the components of LR; the boiler efficiency model is simply an empirical model based on test results.
Now such theories are wonderful things, and the question is rightly posed, but what of the experimental data? As I reported, I have explored the value of these models by comparing their predictions to a wide range of UK data collected at the test plant, about 1500 2 hour long test plant runs, about a dozen different locomotives from different builders, with different design philosophies, plus road testing. The models predict the outcome of these tests remarka
@Firelock76
However, maybe he could have had a chance to fly over the bridge with a “J”, if available that time.
Faux Pax : How I could dare to mess up C. Chaplin with a Buster Keaton Movie. Sorry about that…It was Buster, of course.
you have started one of the most interesting threads on the web, I have long time looking for.
Thank you for sharing and presenting all your interesting data.
Will send you a private mes. for solving your .zip problem, but I do not see any reason for limiting data files to 500kb.
Just try to send it some way, any package, program or file-extension is fine to me.
If you have correspondence with Mr. Wardale, ask him about his dream steam-engine from the past, to “Wardale” it and improving it to next stage-
he will answer you “The Allegheny”.
( source at.co.uk/uploads/Articles%20and%20papers/lr_w3.pdf Sorry link is obsolete and unavailable now, from German magazine )
Hope to help you for input-data, I can scan you the 1943 Big Boy tests results from Kratville, if you do not have the book.
They show in a some nice way, how efficiency goes down, when the engine is hard working with a heavy a train.
Their output looked OK when they were handled as originally suppossed, to take a 3600tons train.
However, long time seeking for an answer, how they did actually handle 20% heavier trains, as a 1948 showsTT shows.
In addition to Farrington, The Big Three, you might want to check Brasher, Santa Fe Locomotive Development. There is quite a bit in it but not in easy to use format. Another series that might be useful is the “Loco Profile” series published by Profile Publications. There are issues on NYC Hudsons, Nord pacifics, LNER A4, the American 4-8-4, and many others. The ultimate of course is La Locomotive a Vapeur, by Andre Chapelon. There is an Engilsh edition translated by G W Carpenter. If anyone knows high efficiency steam, it is Chapelon.
I think it was Churchward that said he could improve the efficiency of any engine by 10% simply by painting the funnel blue. His point was that day to day operation depended much more on correct operating procedues than pedantic design detail. If a crew believe they are being closely watched, they’ll do things right. And of course what’s best depends on whether you want speed, drawbar effort, water economy, simple maintenance, etc.
The objective of the boiler is to produce steam faster than any combination of engine parameters can consume it. The objective of the engine is to produce an effective output using all the steam the boiler can produce. To pass great quantities requires large cross-sections through-out the exhaust path. Higher superheat gives more fluid steam. Numerous designers got the passage part right. Fiddling with just the exhaust outlet is only a part of the answer. High superheat in daily practice really is more a matter of cost and reliability than it is pure engine efficiency.
Having said this, few steam locomotives operated near their maximum for any length of time. The NYC Niagaras were great but for day after day long, high speed runs, you have to give the blue ribbon to the ATSF 4-8-4s.